Sorption materials can take in substances from gaseous or liquid mixtures. If water vapor is extracted (e.g. from ambient air) we describe this as dehumidifying or drying. If ecologically hazardous substances are removed we describe this as cleaning. The generic term for these processes is material separation.
An example of how this is applied is the dehumidification of outside air for the climate control in buildings. Especially in tropical regions the energy consumption for dehumidification is much higher than for cooling. In some cases the dehumidification at constant temperature alone is sufficient to condition the outside air.
A dehumidification system using sorption materials has successfully been realized and installed in the large-scale laboratory of CC TEVT. The warm and humid air from outside is directed through channels of a plate heat exchanger. The walls of the plate heat exchanger are wetted with a thin layer of a concentrated saline solution. In this instance calcium chloride is used as a salt, which can also be used for defrosting roads during winter. The saline solution absorbs water vapor, which dries the outside air. Simultaneously cooler air inside the room flows in a cross-flow configuration through the heat exchanger into the environment. The temperature of the air inside the room is reduced further through direct evaporative cooling. This also cools down the saline solution and the outside air and allows for isothermal dehumidification. Without this cooling mechanism the saline solution would heat up due to absorption and as a consequence the temperature of the outside air would rise as well. After dehumidification the resulting aqueous saline solution is concentrated to its initial level in a desorber through heat input supplied by a solar thermal collector and is returned to the heat exchanger after an intermediate cooling stage. The dehumidification process runs on solar heat and only consumes a fraction of electricity compared to the current technology. Presently worldwide, dehumidification is done almost entirely through electrically driven chillers.
Another sample application is the cleaning and preparation of biogas. If biogas is to be burned in a CHP it must be cleaned beforehand. In order to remove siloxanes, such as benzene, toluene, ethylbenzene, etc., which would lead to solid silicates in the combustion chamber that damage the CHP, solid sorption materials such as activated carbon are used. If the biogas is to be fed into the gas grid its concentration of CO2 has to be reduced to a critical level. This can be achieved with liquid sorption materials like water that absorb CO2 under high pressure and release it to the environment under low pressure (pressure washing).Other materials that can be used are amines, which absorb CO2 at low temperatures and release it at high temperatures (amine washing).
Sorption materials can also be used for different processes that dehumidify, dry or clean a gas. Some examples are air dehumidification in a dish washer, drying of food, flue gas desulfurization and de-pluming or de-steaming.